White-emitting copolymers, representation and use thereof

ABSTRACT

The present invention relates to white-emitting copolymers which are obtained by a combination of blue-, green- and red-emitting repeating units. The copolymers of the invention display better film formation and an improved efficiency when used in polymeric organic light-emitting diodes compared to materials according to the prior art.

RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. 371)of PCT/EP2004/010439 filed Sep. 17, 2004 which claims benefit to Germanapplication 103 43 606.5 filed Sep. 20, 2003.

Wide-ranging research on the commercialization of display and lightingelements based on polymeric (organic) light-emitting diodes (PLEDs) hasbeen carried out for about 12 years.

This development was triggered by the fundamental developments disclosedin EP 423283. Recently, a first albeit simple product (a small displayin a shaver from PHILIPS N.V.) has become available on the market.However, significant improvements are still necessary in order to makethese displays genuinely competitive with the liquid crystal displays(LCDs) which currently dominate the market or to surpass them. Inparticular, it is necessary to provide either polymers for all emissioncolors (red, green, blue) which meet the requirements of the market(color saturation, efficiency, operating life, to name the mostimportant) or to provide white-emitting polymers which meet theserequirements and can be used in conjunction with color filters infull-color devices.

Various classes of materials have been developed as polymers. Thus,poly-para-phenylene-vinylenes (PPVs) are possible for this purpose.Furthermore, polyfluorene and polyspirobifluorene derivatives areanother possibility, as are polymers comprising a combination of thesetwo structural elements. In general, polymers comprisingpoly-para-phenylene (PPP) as structural element are possible for suchuse. Apart from the abovementioned classes, further possibilities are,for example, ladder PPPs (=LPPPs), polytetrahydropyrenes,polyindenofluorenes or polydihydrophenanthrenes.

To produce all three emission colors, it is necessary to polymerizeparticular comonomers into the corresponding polymers (cf., for example,WO 00/46321, WO 03/020790 and WO 02/077060). In this way, it isgenerally possible, starting from a blue-emitting base polymer(“backbone”), to produce the two other primary colors red and green.

The commercialization of both single-color and multicolor or full-colordisplays based on PLEDs is being assessed at present. Single-colorelectroluminescent devices can be produced comparatively simply byprocessing the materials by surface coating from solution (e.g. by spincoating, etc.). The structuring, i.e. the control of the individualpixels, is usually carried out here on the “leads”, i.e. on theelectrodes, for example. In the case of multicolor or full-color displayelements, the use of printing methods (e.g. ink jet printing, offsetprinting, screen printing, etc.) is very probable. That this presentsconsiderable problems is made obvious from the dimensions alone:structures in the region of a few 10 μm at layer thicknesses in therange from less than 100 nm to a few μm have to be produced.

A further possible way of producing full-color displays withsimplification or avoidance of complicated printing techniques is toapply a white-emitting polymer over the entire surface or in astructured fashion and to generate the individual colors therefrom bymeans of a color filter, as is already prior art for liquid crystaldisplays (LCDs).

Furthermore, white-emitting polymers can be used for monochrome whitedisplays. The use of white-emitting polymers as backlight in liquidcrystal displays is also possible, both for monochrome displays and formulticolor displays. In the widest possible use, white emission isgenerally to be used for lighting purposes (illumination), since whiteis most similar to sunlight.

It can thus be seen that there is a great demand for white-emittingpolymers. However, it is difficult or impossible to find a singlechromophore which emits light over the entire visible range. Withoutwishing to be tied to a particular theory for the purposes of theinvention, white cannot be assigned a particular wavelength or aparticular wavelength range as is the case for red, green and blue. Onlyadditive color mixing of, for example, emitted light having the primarycolors red, green and blue or a mixture of complementary colors, forexample blue and yellow, enables the total emitted light to appearwhite.

The best-known white-emitting polymer systems are therefore blends(mixtures) of a blue-emitting polymer and a small proportion of ayellow- to red-emitting polymeric or low molecular weight compound (e.g.U.S. Pat. No. 6,127,693). Ternary blends in which green- andred-emitting polymers or low molecular weight compounds are mixed withthe blue-emitting polymer are also known (e.g. Y. C. Kim et al.,Polymeric Materials Science and Engineering 2002, 87, 286; T.-W. Lee etal., Synth. Metals 2001, 122, 437). A summary of such blends is given byS.-A. Chen et al., ACS Symposium Series 1999, 735 (SemiconductingPolymers), 163. U.S. 2004/0033388 describes white-emitting blendscomprising a blue-emitting polymer together with two or more lowmolecular weight emitters, with the dopants being used in amounts ofless than 0.1% by weight. Here, extremely high voltages are necessaryfor such a system to be of use in practical applications.

All these blends, regardless of whether they are blends with polymers orlow molecular weight compounds, have two critical disadvantages: thepolymers in blends are often not ideally miscible with one another andtherefore tend to give significantly poorer film formation and/or phaseseparation in the film. The formation of homogeneous films, as areessential for use in light-emitting diodes, is frequently not possible.In addition, there is a risk of crystallization or of migration of thelow molecular weight compound, which leads to reduced long-termstability. Phase separation in the device during prolonged operation isalso observed and leads to a reduction in the life and to colorinstabilities. In the case of white-emitting PLEDs, color purity andcolor stability of the device among the most important aspects. Heretoo, blends have a disadvantage, since the individual blend componentsage at different speeds (“differential aging”) and thus lead to a colorshift. Blends are therefore generally less suitable for use in PLEDsthan are copolymers.

Furthermore, white-emitting copolymers whose white emission is made upof a blue-emitting unit in the polymer and an aggregate of these unitswhose emission is shifted in the red direction are also known. However,the efficiency of the emission when using such polymers is so low thatsuch polymers are unusable in practical applications. An example of sucha copolymer is given in U.S. 2003/00081751; the white emission is inthis case made up of the blue emission of a polymer backbone and thered-shifted emission of particular carbazole aggregates of which a largeproportion is present in copolymerized form. Although this avoids thedisadvantages inherent in the abovementioned blends, a cutoff voltage of9 V and an efficiency of only 0.06 cd/A are reported for a devicecomprising such a polymer. However, the document does not teach howhigher efficiencies and reduced cutoff and operating voltages can beachieved using the proposed polymer composition. A further example isgiven by K. L. Paik et al. (Optical Materials 2002, 21, 135). Here too,the red part of the emission is based on an aggregate (exciplex or thelike). The disadvantage here can also clearly be seen, since theemission color is blue at voltages below 13 V and only shifts to whiteat voltages above 13 V. Zhan et al. (Synth. Met. 2001, 124, 323) studieda white-emitting copolymer comprising diethynylfluorene and thiopheneunits, with an exciplex also participating in the emission here. Theexternal quantum efficiency is only 0.01% and electroluminescence canonly be detected above a voltage of 11 V. A white-emitting copolymercomprising oxadiazole, phenylene-vinylene and alkyl ether units isdescribed by Lee et al. (Appl. Phys. Lett. 2001, 79, 308) with theemission being composed of a blue emission of the polymer and a redemission of an excited dimer in this case, too. The maximum efficiencyis only 0.071 cd/A, the operating voltages are very high and thelight-emitting diode displays a high dependence of the color location onthe voltage.

In view of the high voltages and the poor efficiencies of thesepolymers, we assume a disadvantage intrinsically associated withaggregate emission, namely that these act as charge traps. Thesepolymers are all unsuitable for industrial use, since they do notdisplay a stable white emission over a wide voltage range, and alsodisplay very poor efficiencies and require high voltages.

U.S. 2003/224208 describes nonconjugated polymers which have tripletemitters bound in the side chain. It is mentioned that white emissioncan also be produced by use of a plurality of different metal complexesin a polymer. However, this document does not indicate which metalcomplexes can be usefully combined here and, in particular, theproportions in which these complexes have to be present in the polymer,so that a person skilled in the art would not be able to derive anyteachings as to how white emission could be produced from these polymerson the basis of the information given. In particular, white-emittingpolymers are only described as mixtures (blends) of two polymers havingdifferent emission colors in the examples, so that it is obvious that inthis case white emission cannot be produced in a simple manner from asimple polymer.

EP 1424350 describes phosphorescent polymers which comprise blue, greenand red triplet emitters or blue / green and yellow / red tripletemitters and can thus display an overall white emission. However, thisdocument, too, does not indicate which metal complexes can be usefullyemployed here and the proportions in which they are to be used, so thatin this case, too, it is not possible for a person skilled in the art tosuccessfully use the polymers described for white emission in practice.In the single example of white-emitting polymers, only a very smallproportion (1 mol %) of a blue-emitting monomer is used together withgreen- and red-emitting monomers in a nonconjugated matrix derived fromcarbazole. Although white emission is obtained using this polymer,neither efficiency nor operating voltage nor life are indicated, so thatit has to be presumed that these properties are not yet satisfactoryhere and that such a small proportion of a blue-emitting monomer and anonconjugated matrix derived from carbazole are therefore not suitablefor achieving good properties.

WO 03/102109 describes white-emitting copolymers which simultaneouslydisplay phosphorescence from a covalently bound iridium complex andfluorescence from the conjugated main chain of the polymer. A proportionof the triplet emitter of preferably from 0.01 to 5 mol % is indicatedhere. However, all examples report polymers whose proportion ofgreen-emitting triplet emitters is 1 mol % and more, usually even ashigh as 2-4 mol %, so that it may be presumed that the lower proportionis only referred to coincidentally. It is not stated how it is possible,in a targeted manner, to obtain polymers which display whiteluminescence instead of colored phosphorescence, which is likewisedescribed in this patent application with the same proportion of thesame monomers, so that once again a person skilled in the art is able toderive no teachings about the measures which have to be taken to preparewhite-emitting polymers. Thus, examples which report very similarcomplexes in the same concentration in similar polymers, with some ofthese displaying green or red emission and in similar cases displayingwhite emission, are described. Furthermore, it is stated that thecombination of fluorene units with red-emitting triplet emitters alwaysleads to complete energy transfer and thus not to white emission. Thissuggests that it is not possible to obtain good white-emitting polymersin this way, since the proportion of red in the emission spectrum is toolow if no red-emitting units can be used. Although the polymersdescribed in the examples display white emission, the efficiency in thefew examples in which electroluminescence measurements are described isextremely low and is in the range from <0.02 to 0.2 cd/A at operatingvoltages of about 12 V. These polymers are therefore unsuitable forpractical applications.

It can clearly be seen from the above-described prior art that there isnot yet a solution to the problem of obtaining high-quality,white-emitting PLEDs. For this reason, there continues to be a greatneed for white-emitting polymers which display good film formation, havehigh efficiencies and have low operating voltages.

It has now surprisingly been found that the copolymers described in moredetail below display very efficient white emission at good colorcoordinates and a low operating voltage. These polymers and their use inPLEDs are therefore subject matter of the present invention.

The invention provides white-emitting copolymers comprising at least twodifferent repeating units, characterized in that the first repeatingunit, unit B, is present in a proportion of at least 10 mol % anddisplays blue emission and the second repeating unit, unit R, is presentin a proportion of from 0.0005 to 1 mol % and displays red emission,with the proviso that this unit B is not a carbazole when the polymer isa nonconjugated phosphorescent polymer; and with the exception of apolymer comprising the repeating units (a), (b) and (c),

where the content of monomer (b) is in the range from 2.32 to 2.34 mol %and the content of monomer (c) is in the range from 0.174 to 0.176 mol%.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the electroluminesence spectrum of polymer P1 as a functionof the brightness.

FIG. 2 shows the electroluminescence spectrum of polymer P 1 as afunction of the time of operation.

A preferred embodiment of the invention provides white-emittingcopolymers comprising at least three different repeating units,characterized in that the first repeating unit, unit B, is present in aproportion of at least 10 mol % and displays blue emission, the secondrepeating unit, unit G, is present in the polymer in a proportion offrom 0.001 to 3 mol % and displays green emission and the thirdrepeating unit, unit R, is present in a proportion of from 0.0005 to 1mol % and displays red emission.

This description does not rule out the possibility of a nonconjugatedphosphorescent polymer comprising carbazole units when at least 10 mol %of units B which are different from carbazole are present.

In both the above-described copolymers, the proportions of all repeatingunits present, i.e. the units B, the units R, optionally the units G andoptionally further repeating units, add up to 100 mol %.

White emission is defined by the CIE color coordinates x=0.33 and y=0.33(chromaticity coordinates of the Commission Internationale deI'Eclairage of 1931). However, the color impression can displayindividual differences, so that a value which is in the vicinity of thisrange can still give the impression of white emission. For the purposesof the present invention, white emission is therefore an emission whosecolor coordinates lie within an ellipse going through the points havingthe x/y color coordinates of (0.22/0.24), (0.46/0.44), (0.28/0.38) and(0.37/0.28). The polymers of the invention preferably emit white lightwhich is defined by a color location in the chromaticity diagramaccording to CIE 1931 in which the color coordinate x can assume valuesof from 0.28 to 0.38 and the color coordinate y can, independently of x,assume values of from 0.28 to 0.38.

A blue-emitting repeating unit B for the purposes of the presentinvention is defined as follows: a film of the homopolymer of this unitB displays luminescence (fluorescence or phosphorescence) and themaximum of the emission curve of a film of a polymer comprising 10 mol %of this unit B and 90 mol % of2,7-[2′,3′,6′,7′-tetra(2-methylbutyloxy)spirobifluoren]ylene is in awavelength range from 400 to 490 nm.

A green-emitting repeating unit G for the purposes of the presentinvention is defined as follows: the maximum of the fluorescence orphosphorescence curve of a film of a polymer comprising 10 mol % of thisunit G and 90 mol % of2,7-[2′,3′,6′,7′-tetra(2-methylbutyloxy)spirobifluoren]ylene is in awavelength range from 490 to 570 nm.

A red-emitting repeating unit R for the purposes of the presentinvention is defined as follows: the maximum of the fluorescence orphosphorescence curve of a film of a polymer comprising 10 mol % of thisunit R and 90 mol % of2,7-[2′,3′,6′,7′-tetra(2-methylbutyloxy)spirobifluoren]ylene is in awavelength range from 570 to 700 nm.

It may here be explicitly pointed out that for the purposes of thepresent invention mixed colors such as yellow or orange also count asred or green emission depending on their emission maximum.

The limits within which a polymer displays white emission are not to beregarded as rigid. For example, it is possible for a polymer whichcomprises blue-emitting units together with from 0.0005 to 1 mol % ofgreen units whose emission maximum according to the above definition isin the range from about 550 to 570 nm to still display white emissionhaving good color coordinates. Such polymers are also subject matter ofthe present invention.

Preference is given to copolymers in which the proportion of redrepeating units R is less than the proportion of green repeating unitsG. The ratio of red repeating units to green repeating units (units R:G)is particularly preferably in the range from 1:50 to 1:1.1. The ratio ofred repeating units to green repeating units (units R:G) is veryparticularly preferably in the range from 1:20 to 1:2.

The polymers of the invention can be conjugated, partially conjugated ornonconjugated. A preferred embodiment of the invention uses conjugatedor partially conjugated copolymers. A particularly preferred embodimentof the invention uses conjugated copolymers. For the purposes of thepresent invention, conjugated polymers are polymers which have mainlysp²-hybridized (or sp-hybridized) carbon atoms, which may also bereplaced by appropriate heteroatoms, in the main chain. In the simplestcase, this means the alternating presence of double and single bonds inthe main chain. “Mainly” means that naturally occurring defects whichlead to interruptions to the conjugation do not invalidate the term“conjugated polymer”. Furthermore, polymers having, for example,arylamine units, arylphosphine units and/or particular heterocycles(i.e. conjugation via N—, O— or S atoms) and/or organic metal complexes(i.e. conjugation via the metal atom) in the main chain are likewisereferred to as conjugated in the present patent application text. On theother hand, units such as simple (thio)ether bridges, alkylene bridges,ester, amide or imide linkages would clearly be defined as nonconjugatedsegments. For the purposes of the present invention, a partiallyconjugated polymer is a polymer which either has relatively longconjugated sections which are interrupted by nonconjugated sections inthe main chain or has relatively long conjugated sections in the sidechains of a polymer whose main chain is nonconjugated.

The different repeating units of the copolymer can be selected fromvarious groups. These structural units and their syntheses arecomprehensively described in WO 02/077060, WO 03/020790, DE 10337346.2and the literature cited therein.

Blue-emitting repeating units B are typically units which are generallyused as polymer backbone or units which are used as blue emitters. Theseare generally ones which comprise at least one aromatic or otherconjugated structure but do not shift the emission color into the greenor into the red. Preference is given to aromatic structures having from4 to 40 carbon atoms, but also stilbene and tolane derivatives andcertain bis(styryl)arylene derivatives. These are, for example, thefollowing structural elements which may be substituted, for example byone or more groups having from 1 to 40 carbon atoms, or unsubstituted:1,4-phenylene derivatives, 1,4-naphthylene derivatives, 1,4- or9,10-anthracenylene derivatives, 2,7- or 3,6-phenanthrenylenederivatives, 4,4′-biphenylylene derivatives, 4,4″-terphenylylenederivatives, 4,4′-bi-1,1′-naphthylylene derivatives, 4,4′-stilbenederivatives, 4,5-dihydropyrene derivatives, 4,5,9,10-tetrahydropyrenederivatives, fluorene derivatives (e.g. as described in EP 0842208, WO99/54385, WO 00/22027, WO 00/22026, WO 00/46321), spirobifluorenederivatives (e.g. as described in EP 0707020, EP 0894107, WO 03/020790,WO 02/077060), 5,7-dihydrodibenzoxepin derivatives, cis- andtrans-indenofluorene derivatives (e.g. as described in WO 04/041901, EP03014042.0) and 9,10-dihydrophenanthrene derivatives (e.g. as describedin DE 10337346.2). Apart from these classes, ladder PPPs (=LPPPs) orsections of such polymers (e.g. as described in WO 92/18552) and alsoPPPs containing ansa structures (e.g. as described in EP 690086), forexample, are also possible here. Bis(Styryl)arylene derivatives whichare not electron-rich can also be used for this purpose. It can also bepreferred to use a plurality of different blue-emitting repeating unitsB of this type instead of one such unit in a polymer.

If the polymer contains green-emitting repeating units G, these arepreferably units which comprise at least one aromatic or otherconjugated structure and shift the emission color into the green.Preferred structures for green-emitting repeating units G are selectedfrom the group consisting of electron-rich bisstyrylarylenes andderivatives of these structures. Without wishing to be tied to aparticular theory, we presume that electron-pushing substituentsgenerally lead to a green shift in the emission of these units. Furtherpreferred green-emitting repeating units are selected from the groupconsisting of benzothiadiazoles and corresponding oxygen derivatives,quinoxalines, phenothiazines, phenoxazines, dihydrophenazines,bis(thienyl)arylenes, oligo(thienylenes) and phenazines. It is alsopermissible for a plurality of different green-emitting repeating unitsG to be used instead of one such repeating unit, in which case the totalproportion of the green-emitting repeating units G is then not more than3 mol %.

Particularly preferred structures which are suitable as green-emittingrepeating units G are structures of the formulae (I) to (XII), which maybe substituted, for example by one or more organic groups having from 1to 40 carbon atoms, or unsubstituted,

where the symbols and indices used have the following meanings:

-   Y is identical or different on each occurrence and is in each case S    or O;-   Ar is identical or different on each occurrence and is in each case    an aromatic or heteroaromatic ring system which has from 3 to 30    carbon atoms and may be unsubstituted or substituted by fluorine or    by one or more substituents R, OR or NR₂, preferably selected from    the group consisting of phenyls, biphenyls, fluorenes,    spirobifluorenes, thiophenes, furans or pyrroles, with the proviso    that at least one unit Ar in the formulae (IX) and (X) is an    electron-rich aromatic unit or is substituted by electron-rich    substituents; this is preferably achieved by the unit being selected    from among the structures of substituted or unsubstituted    thiophenes, furans or pyrroles or by this unit being a phenyl group    which is substituted by at least one alkoxy group, aryloxy group or    substituted or unsubstituted amino group or a plurality of identical    or different groups of this type;-   R is identical or different on each occurrence and is in each case    H, a linear, branched or cyclic alkyl chain which has from 1 to 22    carbon atoms and in which one or more nonadjacent carbon atoms may    also be replaced by O, S, —CO—O— or —O—CO—O—, where one or more H    atoms may also be replaced by fluorine, or a substituted or    unsubstituted aryl group which has from 5 to 40 carbon atoms and in    which one or more carbon atoms may also be replaced by O, S or N;-   p is identical or different on each occurrence and is in each case    1, 2, 3, 4 or 5, preferably 1, 2 or 3;    and the broken-line bonds indicate the linkage in the polymer; they    are in this case not a methyl group.

As red-emitting repeating units R, preference is given to units whichcomprise at least one aromatic or other conjugated structure and shiftthe emission color into the red. Preferred structures for red-emittingrepeating units R are those in which electron-rich units, for examplethiophene, are combined with green-emitting electron-deficient units,for example quinoxaline or benzothiadiazole. Further preferredred-emitting repeating units R are systems comprising at least four,preferably at least five, fused, substituted or unsubstituted aromaticunits such as rubrenes, pentacenes or perylenes which are preferablysubstituted, or conjugated push-pull systems (systems which aresubstituted by donor and acceptor substituents) or systems such assquarines or quinacridones which are preferably substituted. Here, it isalso permissible for a plurality of different red-emitting repeatingunits R to be used instead of one such repeating unit, with the totalnumber of the red-emitting repeating units R then being not more than 1mol %.

Particularly preferred structures which are suitable as red-emittingrepeating units R are structures of the formulae (XIII) to (XX), whichmay be substituted, for example by one or more organic groups havingfrom 1 to 40 carbon atoms, or unsubstituted,

where the symbols are as defined above.

As blue-, green- and red-emitting structural units B, G and R, it is inprinciple also possible to use units which emit light from the tripletstate, i.e. display electrophosphorescence instead ofelectrofluorescence, which frequently leads to an increase in the energyefficiency, instead of or in addition to the abovementioned units. Theseunits will hereinafter be referred to as triplet emitters. The use ofsuch metal complexes in low molecular weight OLEDs is described, forexample, in M. A. Baldo et al. (Appl. Phys. Lett. 1999, 75, 4-6).Compounds suitable here are firstly compounds which contain heavy atoms,i.e. atoms from the Periodic Table of the Elements having an atomicnumber of more than 36. Compounds comprising d and f transition metalswhich fulfill the abovementioned condition are particularly useful forthis purpose. Very particular preference is given to structural units ofthis type which contain elements of groups 8 to 10 (i.e. Ru, Os, Rh, Ir,Pd, Pt), in particular Ir or Pt. Possible structural units for thepolymers of the invention are various complexes which are described, forexample, in the patent applications WO 02/068435, WO 02/081488, EP1239526 and WO 04/026886. Corresponding monomers which can, for example,be copolymerized by means of Suzuki coupling are described in WO02/068435.

The colors of the complexes are determined first and foremost by themetal used, by the precise ligand structure and by the substituents onthe ligand. Green- and also red- and blue-emitting complexes are allknown. Thus, for example, unsubstituted tris(phenylpyridyl)iridium(III)emits green light, while electron-pushing substituents in the paraposition relative to the coordinating carbon atom (e.g. diarylaminosubstituents) shift the emission into the orange-red. Furthermore,derivatives of this complex which have a modified ligand structure andlead to orange or deep red emission are known. Examples of such ligandsare 2-phenylisoquinoline, 2-benzothienylpyridine and 2-naphthylpyridine.Blue-emitting complexes are obtained, for example, by substituting thetris(phenylpyridyl)iridium(III) skeleton with electron-pullingsubstituents, for example a plurality of fluoro and/or cyano groups.

If, for example, triplet emitters are thus used as red-emitting unitsand units which emit light from the singlet state are used as green- andblue-emitting units, the overall polymer thus displays a mixture ofelectrofluorescence and electrophosphorescence and can display whiteemission if the composition is appropriate. If only triplet emitters areused for all emission colors, the polymer displays onlyelectrophosphorescence. If only singlet emitters are used for allemission colors, the polymer displays only electrofluorescence.

Preference is also given to white-emitting copolymers which comprisefurther repeating units which either display no fluorescence or whosemaximum of the fluorescence curve is in a wavelength range from 400 to490 nm in addition to the abovementioned repeating units. The use ofsuch repeating units can be useful, for example, to aid hole transport,hole injection, electron transport and/or electron injection. For thepurposes of the present patent application text, such structuralelements are as follows: if homopolymers or oligomers of thesestructural elements were produced, these would have, at least for onecharge carrier, i.e. either for electrons or holes, a higher chargecarrier mobility than is the case for a polymer which consistsexclusively of structural elements described above as “blue-emitting” orbackbone structures. The charge carrier mobility (measured in cm²/(V.s))is preferably greater by a factor of at least 10, particularlypreferably at least 50.

Repeating units which improve hole transport and/or hole injection arepreferably selected from the group consisting of triarylaminederivatives, triarylphosphine derivatives, benzidine derivatives,tetraarylene-para-phenylenediamine derivatives, thianthrene derivatives,dibenzo-p-dioxin derivatives, phenoxathiin derivatives, carbazolederivatives, azulene derivatives, thiophene derivatives, pyrrolederivatives, furan derivatives and further O—, S— or N-containingheterocycles having a high HOMO (HOMO=highest occupied molecularorbital); these may each be substituted, for example by one or moreorganic groups having from 1 to 40 carbon atoms, or unsubstituted. Theseunits preferably lead to a HOMO in the polymer of less than 5.8 eV(relative to vacuum), particularly preferably less than 5.5 eV.

Structural elements which improve electron transport and/or electroninjection are preferably selected from the group consisting of pyridinederivatives, pyrimidine derivatives, pyridazine derivatives, pyrazinederivatives, triarylboranes, oxadiazole derivatives, quinolinederivatives, triazine derivatives and further O—, S— or N-containingheterocycles having a low LUMO (LUMO=lowest unoccupied molecularorbital); these may be substituted, for example by one or more organicgroups having from 1 to 40 carbon atoms, or unsubstituted. These unitspreferably lead to a LUMO in the polymer of greater than 2.7 eV(relative to vacuum), particularly preferably greater than 3.0 eV.

Further structural elements can be used to aid singlet-triplet transferin the polymer. Such groups are used, in particular, when at least oneof the red-, green- and/or blue-emitting structural units comprises atriplet emitter. Groups preferred for this purpose are carbazole units,in particular bridged carbazole dimer units as described in theunpublished patent applications DE 10304819.7 and DE 10328627.6.

It has surprisingly been found that stable white emission is achievedparticularly well when using an unexpectedly small proportion of green-and red-emitting repeating units G and R. Thus, the proportion ofblue-emitting repeating units B is preferably at least 20 mol %, theproportion of green-emitting repeating units G is preferably up to amaximum of 2 mol %, the proportion of red-emitting repeating units R ispreferably from 0.0005 to 0.5 mol % and the ratio of red-emittingrepeating units to green-emitting repeating units (units R:G) ispreferably in the range from 1:50 to 1:1.1.

Particular preference is given to the proportion of blue-emittingrepeating units B being at least 30 mol %, the proportion ofgreen-emitting repeating units G being from 0.005 to 1 mol %, theproportion of red-emitting repeating units R being from 0.001 to 0.3 mol% and the ratio of red-emitting repeating units to green-emittingrepeating units (units R:G) preferably being in the range from 1:30 to1:1.5.

Very particular preference is given to the proportion of blue-emittingrepeating units B being at least 50 mol %, the proportion ofgreen-emitting repeating units G being from 0.01 to 0.5 mol %, theproportion of red-emitting repeating units R being from 0.002 to 0.1 mol%, in particular from 0.002 to 0.05 mol %, and the ratio of red-emittingrepeating units to green-emitting repeating units (units R:G) preferablybeing in the range from 1:20 to 1:2. It can also be preferred that theproportion of blue-emitting repeating units B in the polymer is up to 99mol % or more.

Without wishing to be tied to a specific theory, we presume that thesurprisingly good partial energy transfer from blue to green and fromgreen to red and the consequently surprisingly low proportion of red-and green-emitting units in the conjugated polymers results from a highconjugation along the polymer chain. In polymer blends, the proportionsof the red-emitting polymer (and, if present, the green-emittingpolymer) are frequently significantly higher.

The polymers of the invention generally have from 10 to 10 000,preferably from 50 to 5000, particularly preferably from 50 to 2000,repeating units.

The copolymers of the invention can have random or block structures orcan have a plurality of these structures arranged alternately. The wayin which copolymers having block structures can be obtained is, forexample, comprehensively described in the unpublished patent applicationDE 10337077.3. It is also possible to incorporate particular units, forexample red- and/or green-emitting units, as end group at the ends ofthe polymer chain. The use of various structural elements enablesproperties such as solubility, solid state morphology, color, chargeinjection properties and charge transport properties, electroopticalcharacteristics, etc., to be set.

The polymers of the invention are generally prepared by polymerizationof the monomers. The type of polymerization reaction is not critical.However, some types which will lead to formation of C-C bonds have beenfound to be particularly useful, in particular for conjugated polymers:

(A) polymerization by the SUZUKI method,

(B) polymerization by the YAMAMOTO method,

(C) polymerization by the STILLE method.

The way in which the polymerization can be carried out by means of thesemethods and the way in which the polymers can be separated off from thereaction medium and purified are described in detail in, for example, WO04/037887. The synthesis of partially conjugated or nonconjugatedpolymers can also be carried out by these methods, by using appropriatemonomers which are not completely conjugated. However, other syntheticmethods as are generally well-known from polymer chemistry, for examplepolycondensations or polymerizations in general which proceed, forexample, via reaction of alkenes and lead to polyethylene derivatives inthe broadest sense which then have the chromophores bound in the sidechains, are also possible for partially conjugated or nonconjugatedpolymers.

Compared to the abovementioned white-emitting polymer blends and theabovementioned white-emitting copolymers, the copolymers of theinvention have the following surprising advantages:

-   (1) The copolymers of the invention form significantly more    homogeneous films compared to polymer blends of the prior art. No    phase separation can be observed in them and they are therefore also    more long-lived in use. They are therefore better suited for use in    PLEDs.-   (2) The copolymers of the invention have significantly higher    luminous efficiencies and significantly lower operating voltages in    use, in particular compared to polymers whose white emission is    based on aggregates. However, the efficiency is also greater by a    factor of up to more than 50 compared to polymers which    simultaneously display fluorescence and phosphorescence, as    described, for example, in WO 03/102109, and in which the proportion    of the green emitter is significantly higher than in the polymers of    the invention. This is of tremendous importance since it makes it    possible, firstly, to achieve the same brightness at a lower energy    consumption, which is of particular importance in mobile    applications (displays for mobile telephones, PDAs, etc.) which rely    on batteries and accumulators. Conversely, higher brightnesses are    obtained at the same energy consumption, which is of interest for,    for example, lighting applications.-   (3) The ability to obtain pure white emission in the case of the    copolymers of the invention is at least the same or better than the    prior art. In particular, in the case of the copolymers of the    invention, the color point is shifted only slightly as a function of    the operating voltage or as a function of the time of operation,    which was in no way to be expected and is therefore surprising. This    is essential for the use of these copolymers.-   (4) The efficiency remains virtually constant even at high voltages    and thus high brightnesses, as a result of which these polymers are    also suitable for use in display elements having passive matrix    control.

It can also be preferred to use the polymers of the invention not as apure substance but as a mixture (blend) together with any furtherpolymeric, oligomeric, dendritic or low molecular weight substances.These can, for example, improve charge transport and/or the chargeequilibrium or influence the transfer from the singlet state to thetriplet state or emit themselves. Thus, for example, it can be preferredto mix green-emitting compounds into a polymer comprising blue- andred-emitting units in order to increase the green component in thespectrum. However, electronically inactive substances can also be usefulfor influencing, for example, the morphology of the polymer film formedor the viscosity of polymer solutions. Such blends are therefore alsosubject matter of the present invention.

The invention further provides solutions and formulations comprising oneor more copolymers or blends according to the invention in one or moresolvents. The way in which polymer solutions can be prepared isdescribed, for example, in WO 02/072714, WO 03/019694 and the literaturecited therein. These solutions can be used for producing thin polymerlayers, for example by surface coating methods (e.g. spin coating) or byprinting methods (e.g. ink jet printing, screen printing, etc.).

The copolymers and blends according to the invention can be used inPLEDs. The way in which PLEDs can be produced is describedcomprehensively as a general process in WO 04/037887. This has to beadapted appropriately for the individual case. As stated above, thepolymers of the invention are very particularly suitable aselectroluminescence materials in the PLEDs or displays produced in thisway.

For the purposes of the invention, electroluminescence materials arematerials which can be used as active layer in a PLED. The term “activelayer” means that the layer is capable of emitting light on applicationof an electric field (light-emitting layer) and/or that it improves theinjection and/or transport of positive and/or negative charges (chargeinjection layer or charge transport layer).

The invention therefore also provides for the use of a copolymer orblend according to the invention in a PLED, in particular aselectroluminescence material. The copolymers of the invention arepreferably used in the emitting layer.

The invention thus likewise provides a PLED having one or more activelayers of which at least one comprises one or more polymers or blendsaccording to the invention. The active layer can, for example, be alight-emitting layer and/or a charge transport layer and/or a chargeinjection layer, preferably a light-emitting layer.

One embodiment of the invention provides for the use of a PLED accordingto the invention in a monochrome white-emitting display.

A further embodiment of the invention provides for the use of a PLEDaccording to the invention in a monochrome color, multicolor orfull-color display in which the color is produced by use of a colorfilter on the white-emitting PLED.

A further embodiment of the invention provides for the use of a PLEDaccording to the invention for lighting purposes.

A further embodiment of the invention provides for the use of a PLEDaccording to the invention as backlight in a liquid crystal display(LCD).

Thus, the invention further provides white-emitting displays comprisinga PLED according to the invention, color, multicolor or full-colordisplays using a color filter on a PLED according to the invention,lighting elements comprising a PLED according to the invention andliquid crystal displays comprising a PLED according to the invention asbacklight.

The present patent application text and also the examples below aredirected at the use of polymers or blends according to the invention inPLEDs and the corresponding displays. The present invention can also bereadily applied without a further inventive step to, for example,white-emitting dendrimers or oligomers. Likewise, a person skilled inthe art will be able, without having to make an inventive step, toutilize the polymers or blends according to the invention for furtheruses in other electronic devices, e.g. for organic solar cells (O-SCs),organic laser diodes (O lasers), organic integrated circuits (O-ICs), inorganic field effect transistors (O-FETs) or in organic thin filmtransistors (O-TFTs), to name only a few applications. The use of thepolymers or blends according to the invention in the correspondingdevices and also the devices themselves are likewise subject matter ofthe present invention.

The present invention is illustrated by the following examples withoutbeing restricted thereto. A person skilled in the art will be able toprepare further organic semiconductors according to the invention anduse these in organic electronic devices on the basis of the informationgiven in the description and the examples presented without having tomake a further inventive step.

EXAMPLES Example 1 Monomer Syntheses

The structures of the monomers used for the polymers according to theinvention are depicted below. Their emission color in the polymer (inaccordance with the definition in the description) is likewise noted.The syntheses are described in WO 03/020790 and DE 10337346.2.

Example 2 Polymer Syntheses

The polymers were synthesized by SUZUKI coupling as described in WO03/048225. The composition of the polymers P1 to P9 synthesized(Examples 4 to 12) is summarized in Table 1.

Example 3 Production of the PLEDs

All polymers were examined for use in PLEDs. The PLEDs were in each casetwo-layer systems, i.e. substrate//ITO//PEDOT//polymer//cathode. PEDOTis a polythiophene derivative (from H. C. Starck, Goslar). Ba/Ag (fromAldrich) was used as cathode in all cases. The way in which PLEDs can beproduced has been comprehensively described in WO 04/037887 and theliterature cited therein.

The most important device properties of the polymers according to theinvention (color, efficiency, operating voltage, life) are shown inTable 1.

As can easily be seen from this data, the efficiency of all the polymersaccording to the invention is a number of times the efficiency of thecopolymers according to the prior art, and the operating voltages arealso significantly lower. Thus, for example, an efficiency of 0.06 cd/Ais reported for the copolymer in U.S. 2003/00081751, from which it canbe seen that the copolymers according to the invention surpass the priorart by a factor of up to more than 100. A cutoff voltage of 9 V isreported for this polymer according to the prior art, while the polymersaccording to the invention generally have voltages in the order of only4-5 V at 100 cd/m². The efficiency is likewise a number of times as highas that of polymers according to the prior art which contain asignificantly higher proportion of a green-phosphorescing emitter (WO03/102109) and display an overall white emission.

TABLE 1 Examples 4 to 12: Properties of various white-emittingcopolymers P1 to P9 according to the invention. Proportion of monomersin the polymerization [mol %] Electroluminescence Further GPC^(a) Max.Eff.^(b) U^(c) CIE Ex. Poly. M1 M2 M3 M4 M5 M6 M7 M8 M9 monomer M_(w)M_(n) [cd/A] [V] coordinates^(d) Life^(e) [h] 4 P1 50 39.88 0.1 0.02 10672 225 7.89 4.4 0.37/0.39 1100 5 P2 50 39.88 0.1 0.02 10 853 125 6.504.2 0.32/0.32 450 6 P3 50 39.88 0.1 0.02 10 95 37 5.20 5.6 0.36/0.38 4507 P4 50 39.88 0.1 0.02 10 317 101 8.25 4.2 0.40/0.41 2500 8 P5 50 29.980.02 10  10 M11 501 152 5.02 4.3 0.31/0.32 750 9 P6 50 29.94 0.05 0.0110  10 M11 762 108 7.85 4.1 0.37/0.42 1400 10 P7 50 39.88 0.02 10 0.1M10 983 201 4.69 4.5 0.30/0.27 n. d. 11 P8 50 39.88 0.1 10 0.02 M12  283105 7.16 4.0 0.32/0.44 1600 12 P9 50 29.88 0.1 0.02 10  10 M11 624 1468.06 3.9 0.43/0.44 10000 ^(a)GPC measurements: THF; 1 ml/min, Plgel 10μm Mixed-B 2 × 300 × 7.5 mm², 35° C., Rl detection calibrated againstpolystyrene; figure reported in kDa. ^(b)Max. Eff.: Maximum efficiency,measured in cd/A. ^(c)Voltage at a brightness of 100 cd/m². ^(d)CIEcoordinates: Color coordinates of the Commission Internationale del'Eclairage 1931. ^(e)Life: Time for the brightness to drop to 50% ofthe initial brightness (extrapolated to an initial brightness of 100cd/m²).

Example 13 Dependence of the Emission Color on the Brightness

For polymer P1 (Example 4), the emission color was measured as afunction of the brightness at two different brightnesses (100 cd/m² and2000 cd/m²). For practical use, it is important that the color changesonly little as a function of the brightness. The electroluminescencespectra obtained are shown in FIG. 1:

It can be seen that although the emission in the red region of thespectrum decreases somewhat at higher brightness, this color shift issmall (change in the color coordinates from x/y 0.37/0.39 at 100 cd/m²to x/y 0.35/0.42 at 2000 cd/m²). This color shift can be tolerated, andthe polymer can be regarded as mostly color constant as a function ofthe brightness or the operating voltage. This is a significant advantagecompared to copolymers according to the prior art. Thus, for example, K.L. Paik et al., Optical Materials 2002, 21, 135, describes a polymerwhich displays white emission at voltages above 13 V (which is in itselfunusable in practical applications), while below this voltage theemission color is blue, so that there is an extreme dependence of theemission color on the operating voltage (and thus also on thebrightness).

Example 14 Emission Color as a Function of the Time of Operation

For polymer P1 (Example 4), the emission color was determined as afunction of the time of operation. For this purpose, theelectroluminescence spectrum of a freshly constructed PLED was measured.The PLED was then operated at a constant current density (10 mA/cm²)until the brightness had dropped to 50% of the initial brightness, andthe electroluminescence spectrum was measured again. The two spectra areshown in FIG. 2:

It can be seen that the spectrum is virtually unchanged as a function ofthe time of operation (change in the x/y color coordinates from0.37/0.39 before operation to 0.38/0.40 after operation), so that theemission color is constant over the time of operation. This is a furtheressential aspect for practical use of the polymer. Here too, thepolymers according to the invention offer a decisive advantage overpolymers and in particular blends according to the prior art. Blends inparticular are known for the individual blend components aging atdifferent rates during operation (“differential aging”), so that thecolor often shifts considerably during the time of operation. Suchblends are therefore not usable for practical applications. Thus, forexample, a white-emitting blend comprising a blue polymer (comprising 50mol % of M1, 37.5 mol % of M2 and 12.5 mol % of M9) into which 0.4% ofan orange PPV (polyphenylene-vinylene) have been mixed displays initialx/y color coordinates of 0.29/0.37. After operation of the PLED, thiscolor shifts to the color coordinates 0.36/0.45. Such a color shiftcannot be tolerated in practical use.

1. The white-emitting copolymer comprising at least three differentrepeating units, characterized in that the first repeating unit, unit B,is present in a proportion of at least 10 mol % and displays blueemission, the second repeating unit, unit G, is present in the polymerin a proportion of from 0.001 to 3 mol % and displays green emission andthe third repeating unit, unit R, is present in a proportion of from0.0005 to 1 mol % and displays red emission with the proviso that thisunit B is not a carbazole when the polymer is a nonconjugatedphosphorescent polymer; and with the exception of a polymer comprisingthe repeating units (a), (b) and (c),

where the content of monomer (b) is in the range from 2.32 to 2.34 mol %and the content of monomer (c) is in the range from 0.174 to 0.176 mol%.
 2. The copolymer as claimed in claim 1, characterized in that theproportion of red repeating units R is less than the proportion of greenrepeating units G.
 3. The copolymer as claimed in claim 2, characterizedin that the ratio of red repeating units to green repeating units (unitsR:G) is from 1:50 to 1:1.1.
 4. The copolymer as claimed in claim 1,characterized in that the green-emitting repeating unit G is selectedfrom the group consisting of electron-rich bis(styryl)arylenes andcorresponding extended structures, beuzothiadiazoles, quinoxalines,phenothiazines, dihydrophenazines, bis(thienyl)arylenes,oligo(thienylenes), phenazines and corresponding derivatives containingoxygen instead of sulfur.
 5. The copolymer as claimed in claim 4,characterized in that the green-emitting repeating units G are selectedfrom the group consisting of the units of the formulae (I) to (XII),which may be substituted or unsubstituted:

where the symbols and indices used have the following meanings: Y isidentical or different on each occurrence and is in each case S or O; Aris identical or different on each occurrence and is in each case anaromatic or heteroaromatic ring system which has from 3 to 30 carbonatoms and may be unsubstituted or substituted by fluorine or by one ormore radicals R, OR or NR₂, with the proviso that at least one unit Arin the formulae (IX) and (X) is an electron-rich aromatic unit or issubstituted by electron-rich substituents; R is identical or differenton each occurrence and is in each case H, a linear, branched or cyclicalkyl chain which has from 1 to 22 carbon atoms and in which one or morenonadjacent carbon atoms may also be replaced by O, S, —CO—O— or—O—CO—O—, where one or more H atoms may also be replaced by fluorine, ora substituted or unsubstituted aryl group which has from 5 to 40 carbonatoms and in which one or more carbon atoms may also be replaced by O, Sor N; p is identical or different on each occurrence and is in each case1, 2, 3, 4 or 5; and the broken-line bonds indicate the linkage in thepolymer.
 6. The copolymer as claimed in claim 1, characterized in thatunits which display electrophosphorescence instead ofelectrofluorescence are used as blue-, green- and/or red-emittingrepeating units B, G and/or R.
 7. The copolymer as claimed in claim 6,characterized in that these units comprise elements having an atomicnumber of more than
 36. 8. The copolymer as claimed in claim 7,characterized in that these elements are selected from among elements ofgroups 8 to 10 of the periodic table.
 9. The copolymer as claimed inclaim 1, characterized in that more than one blue-emitting repeatingunit B is used and/or that more than one green-emitting repeating unit Gis used, with the total proportion of green-emitting repeating units Gbeing not more than 3 mol %, and/or that more than one red-emittingrepeating unit R is used, with the total proportion of red-emittingrepeating units R being not more than 1 mol %.
 10. The copolymer asclaimed in claim 1, characterized in that the proportion ofblue-emitting repeating units B is at least 20 mol %, the proportion ofgreen-emitting repeating units G is not more than 2 mol % and theproportion of red-emitting repeating units R is from 0.0005 to 0.5 mol %and the ratio of red-emitting repeating units to green-emittingrepeating units (units R:G) is in the range from 1:50 to 1:1.1.
 11. Ablend comprising at least one copolymer as claimed in claim 1 and atleast one further polymeric, oligomeric, dendritic or low molecularweight compound.
 12. A solution or formulation comprising one or morecopolymers or blends as claimed in claim 1 in one or more solvents. 13.A polymeric light-emitting diode (PLED) having one or more active layersof which at least one comprises a copolymer or blend as claimed inclaim
 1. 14. A white-emitting display comprising a PLED as claimed inclaim
 13. 15. A color, multicolor or full-color display in which thecolor is produced by use of a color filter on a white-emitting PLED asclaimed in claim
 13. 16. A lighting element comprising a PLED as claimedin claim
 13. 17. A liquid crystal display (LCD) comprising awhite-emitting PLED as claimed in claim 13 as backlight.
 18. An organicsolar cell, organic laser diode, organic integrated circuit, organicfield effect transistor or organic thin film transistor comprising atleast one polymer or blend as claimed in claim
 1. 19. The copolymer asclaimed in claim 7, characterized in that these elements are Ru, Os, Rh,It, Pd or Pt.